We are investigating the effect of alteration of lipid and protein profile on biochemical and biophysical properties of the membrane. In in situ studies effects of modification of the paraffinic portion and sterol content on growth and biosynthetic adaptability of yeast and also transport and activity of membrane-bound proteins in membranes isolated from them are being examined. In in vitro studies the effect of simple model polypeptides on the biophysical properties of yeast lipid liposomes such as fluidity, osmotic sensitivity, permeability, and volume are being studied. These experiments are carried out in order to delineate principles governing lipid-protein interactions and membrane basis of membrane diseases.